In order to assess the role of cellular and viral oncogenes in the mechanisms of control of cell growth, we developed serum-free culture conditions for NIH/3T3 cells, a murine contact-inhibited fibroblast cell line, which has been shown to be susceptible to DNA transfection and is therefore suitable for gene transfer experiments. Epidermal growth factor (EGF) was found to be the major requiement for NIH/3T3 growth in our defined media. We therefore tried to assess whether expression of viral oncogenes or deregulation of normal cellular gene expression in NIH/3T3 cells could alter their EGF requirement. TGF Alpha, v-fos and v-erbB expression were found to release NIH/3T3 cells form EGF dependence, whereas overexpression of the nuclear oncogene pp53 did not alter their growth factor requirements. Expression of TGF Alpha was found to affect EGF requirement in a cell-density dependent fashion, whereas v-fos-transformed NIH/3T3 could grow without EGF at clonal dilutions. Similar experiments are in progress with v-erbB transformed NIH/3T3 cells.